I don’t have any experience in material patching.

Heres the full story:
there was a chip on the right drop out axle contact face. So I sanded the left one to match the depth of the chip so that the rim can sit centered. However that leaves dead space behind the axle on the left drop out which the wheel is free to slide back into and go off center again

the easy solution is to patch that dead space in the left drop out, the complete solution is to patch the chip on the right as well as restore the original material on the left